Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 10-01-2013, 15:14   #271
Moderator
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,894
Images: 1
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by wolfenzee View Post
.................... Boating is not a "rich man's sport", those of us who cannot afford the latest greatest fanciest name brand, realize we can function quite comfortably on extremely limited budgets with out...and have no problem doing so.
True, but also keep in mind that an extremely accurate GPS costs less than a fairly accurate sextant. I agree that there is a huge amount of overpriced, color monitor, big screen, touch pad, interfaced, multi-screend stuff on the market, It is very easy to pay a modest sum for the best data if you are not one who swoons over glitz!
__________________

__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 10-01-2013, 15:25   #272
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
I think there is a difference between theoretical vector calculations and real life and that lies at the heart of this issue. As an engineer I am familiar with vector addition , and as an aside the " ant" issue is more easily handled using such vectors. Mathematically there is no argument , a summation of all vectors provides a " proper course"

Of course as Dockhead ( I have to be very careful Dockhead with my iphone spelling ! ) himself points put , as the situation gets more complex or the information less reliable the theoretical process develops " implementation" issues. A process familiar to any engineer.

The second issue is of course that we do this computation in an attempt to gain speed. Ie time to destination. But the method only provides advantages in certain circumstances, ie when the track method is at its most inefficient. I have started to investigate how the " advantage " goes from zero to maximum depending on the variables. The advantage grows to maximum in the symmetrical tide example, from zero when the tide is aligned with the track. Obviously the tidal drift and vessel speed are also big influencers.

Outside my home waters, I find myself often with few information sources other then that which can be observed and what is commonly known. I never use track mode anyway. I plot waypoints ahead and use bearing to waypoint for the AP. I can usually intuitively place the WP to counter what I know of the stream.

I personally, to answer you query, don't like large XTEs, because based on experience ( a) with the total passage CTS method , you really don't have a handle on the ground track. The maximum XTE will occur somewhere where you think , but errors in speed, tack angles , wave motion, excessive leeway all add a degree of error. I prefer to break the voyage into shorter sections consistent with a the general tidal stream, so I might run a 2,4or 6 hour triangle depending. Hence my XTE remains less, but obviously I am sacrificing " advantage " in complicated tidal vectors this is about as much as you can do anyway.

Furthermore my experience is that , plotting harbours of refuge , course changes or tack changes further adds significant complexity. Being. " reasonably " close to my rhumb aids this.

Again I believe as re said the key to a good navigator is applying theory and tools in the best practical way.

I've watched for many years , candidates in my classes , computing vectors , reading tidal stream atlas and etc , yet none actually know how to get the boat from A to B. no more then the celestial classes, where everything can be done on a nice stable desk , yet at sea , getting the sight in a heaving boat, and holding back the sea sicknesses as you scribble on a rolling chart table ! .



Ps in relation to the sat compass, its a great pity that they integrate the two antennas into the one housing. In my prototype I use two separate mushroom antennas , so that the installation is quite space efficient.

Good luck with all the electronics.

Dave
__________________

__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 10-01-2013, 15:49   #273
Moderator
 
nigel1's Avatar

Cruisers Forum Supporter

Join Date: Oct 2009
Location: Manchester, UK
Boat: Beneteau 473
Posts: 5,182
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by Andrew Troup View Post
If there is good data perhaps it might be worthwhile if you are towing a rig whilst expending multiple megawatts, or some other situation where the old adage "TIM IS MONY" holds spectacularly true.
On a tow a few months ago, Hull to Rotterdam, once clear of the banks and oil/gas fields, there is a 70 mile run where the tidal stream is close to right angles to the rhumb line.
By allowing for the stream, (within limits) estimated I saved about 2 hours on that leg. Two hours roughly equates to 5000 litres of gas oil. No big deal to the oil company, but gives a sense of achievement, and its a lot less crap pushed out of the exhaust.
__________________
Nigel
Beneteau 473
Manchester, UK
nigel1 is online now   Reply With Quote
Old 10-01-2013, 15:55   #274
Moderator
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,894
Images: 1
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by goboatingnow View Post
.................... Mathematically there is no argument , a summation of all vectors provides a " proper course"

...............I personally, to answer you query, don't like large XTEs ............ so I might run a 2,4or 6 hour triangle depending. Hence my XTE remains less, but obviously I am sacrificing " advantage " in complicated tidal vectors this is about as much as you can do anyway..............Dave
Please excuse my chopping of your post, but I was interested in this idea of preference for the smaller 2 ,4 or 6 hour triangles to decrease XTE. You mention the problem of complicating the data. but, "this is about as much as you can do anyway". Can't we all recognize that the GPS simply continues to decrease the triangle and the XTE beyond our ability to complete the calculations? Is there a fear among instructors of navigation that over reliance on this aide will prevent people from understanding navigation? I do believe that the dependance on GPS will cause many to remain ignorant, but I can't allow this to cause me not to use the tool. This reminds me of the worry about our young students use of calulators to the point that they will not be able to perform math functions with their own knowledge. I agree with the concern, but I'm not in agreement with avoiding the elctronic tools.
__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 10-01-2013, 16:22   #275
Registered User

Join Date: Feb 2012
Posts: 2,441
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by wolfenzee View Post
The best answer I can see for the "thread starter":
People in this culture are "shackled" by what marketing says we should do/buy. It is the foundation of our economy. It is also why boating is thought to be so expensive. Boating is not a "rich man's sport", those of us who cannot afford the latest greatest fanciest name brand, realize we can function quite comfortably on extremely limited budgets with out...and have no problem doing so.
Well, as the 'thread starter', I do think that's an answer to a different question. I was not speculating about the merits of one method vs another, but about their essential nature.

So while yours is an answer to a question which has been argued in this thread, the questions I was asking were: what is navigation, and if it's what I think it is, why do we spend so little time talking about things which pertain to navigation?

Which seems eventually to have accidentally resulted in us talking about things which pertain to navigation, which seems to me like a good outcome.
__________________
Andrew Troup is offline   Reply With Quote
Old 10-01-2013, 16:30   #276
Registered User

Join Date: Jul 2006
Posts: 3,949
Re: Distinct Activities: Shackled by a Common Name?

Good discussion about dealing with current. Strangely, I think I did better in the past crossing the Gulf Stream to the Bahamas or back, prior to GPS, when I used basic tables that were published in the various cruising guides of the day. Today, I find myself watching the GPS instead of just sailing the dang course I should be. Old guidebooks were full of useful knowledge that is no longer published. It's one reason I love to use Eldridge's Tide and Pilot Book in New England. It is full of very useful old-timey advice and tricks that date back to the old sailing ship days that can still be very helpful even with all the electronics.
__________________
Kettlewell Cruising
Kettlewell is offline   Reply With Quote
Old 10-01-2013, 16:53   #277
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Quote:
Originally Posted by CaptForce

Please excuse my chopping of your post, but I was interested in this idea of preference for the smaller 2 ,4 or 6 hour triangles to decrease XTE. You mention the problem of complicating the data. but, "this is about as much as you can do anyway". Can't we all recognize that the GPS simply continues to decrease the triangle and the XTE beyond our ability to complete the calculations? Is there a fear among instructors of navigation that over reliance on this aide will prevent people from understanding navigation? I do believe that the dependance on GPS will cause many to remain ignorant, but I can't allow this to cause me not to use the tool. This reminds me of the worry about our young students use of calulators to the point that they will not be able to perform math functions with their own knowledge. I agree with the concern, but I'm not in agreement with avoiding the elctronic tools.
I don't beleive anyone is suggesting that, but as its pointed out. GPS simply used within thinking does cause inefficiencies. But many accept that in the face of simplicity. To each his own.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 10-01-2013, 17:03   #278
Moderator
 
Seaworthy Lass's Avatar

Cruisers Forum Supporter

Join Date: Oct 2008
Boat: Aluminium cutter rigged sloop
Posts: 12,811
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by Andrew Troup View Post
In reply to Dockhead: From your other post, you make the point "But not necesssarily perpendicularly across." ... I was never under that illusion - I understood that the perpendicular solution only works when the current sets cancel out over the duration of the passage.

What I'm saying is that if the belt slews through an intermediate angle for part of the crossing (lets say it slews 30 deg CW), in order to follow a straight line drawn on the belt, an ant who is unfortunate enough to be relying on a compass will have to correct his heading by adding 30 degrees for the duration of the slew......
This has been a very active thread today! Just catching up with the posts after a super busy day ashore, but 2am isn't the most conducive time for clear thinking (at least not for me LOL).

Andrew, the ant follows a non perpendicular path not only if the current set does not cancel out, but also if the current is not perpendicular to the course for all or part of the trip. I think that helps solve the issue of the belt slewing 30 degrees along the way.

Not sure what happens if the belt rotates past 180 degrees, I would have to think about that.
__________________
"The cure for anything is salt water: sweat, tears or the sea." Isak Dinesen
"To me the simple act of tying a knot is an adventure in unlimited space." Clifford Ashley
Seaworthy Lass is offline   Reply With Quote
Old 10-01-2013, 17:36   #279
Registered User

Join Date: Feb 2012
Posts: 2,441
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by Seaworthy Lass View Post
...

Andrew, the ant follows a non perpendicular path not only if the current set does not cancel out, but also if the current is not perpendicular to the course for all or part of the trip.
I find it hard to follow this train of thought partly because it has one foot in the sea and one on the belt, and partly because you've used "course" in a way which could mean several different things.

Sticking with the ant on the belt (and forgetting about a slewing belt for the moment: treat it as a metaphor for a current which flows either E or W) I was wrong to say that the perpendicular solution only works when the current sets cancel out.
In fact the perpendicular solution works whenever the nett effect of the current sets result in a perpendicularly minded ant arriving at the far side of the belt at the desired exit point. If the exit point is not opposite the entry point, the nett total set needs to be sufficient to carry the ant sideways to line up on exit.

Quote:
Originally Posted by Seaworthy Lass View Post
...I think that helps solve the issue of the belt slewing 30 degrees along the way.

Not sure what happens if the belt rotates past 180 degrees, I would have to think about that.
The issues with the belt slewing 30 degrees are

1) a straight path on the belt is no longer achieved by following a constant compass heading

2) The metaphor of the belt starts to fall apart for reasons internal to the metaphor (ie not needing explanation which resorts to the real situation of sea and current).

I gave an example above of how it fails completely for a 90 deg slew:
in the 30 deg slew instance, (assuming it slews about the location of the ant at that moment, which has to be the case or the ant will magically be whisked to a new set of real world coordinates) the destination point is now no longer at the edge of the belt

It's either underneath it or (worse still) away from it, so again the metaphor fails.

There may be others, but I think that's enough to disqualify it.

But I think it has served its purpose by exposing what seems to be an incompatibility between the 'constant heading' tactic and rotary current scenarios, as I spelled out above for a current which turns through 90 degrees when the ant's about half way there.
__________________
Andrew Troup is offline   Reply With Quote
Old 10-01-2013, 17:42   #280
cruiser

Join Date: Dec 2012
Location: Seattle
Posts: 1,130
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by Seaworthy Lass View Post
Not sure what happens if the belt rotates past 180 degrees, I would have to think about that.
Squashed ant.

"Former Ant."

"Late Ant."

"The Ant Formerly Known as 'Alive'."

"Dead Ant."

"Ant Soup."

"Anteater Blueplate Special."
__________________
Jammer Six is offline   Reply With Quote
Old 10-01-2013, 17:56   #281
Moderator
 
Seaworthy Lass's Avatar

Cruisers Forum Supporter

Join Date: Oct 2008
Boat: Aluminium cutter rigged sloop
Posts: 12,811
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by Jammer Six View Post
Squashed ant.

"Former Ant."

"Late Ant."

"The Ant Formerly Known as 'Alive'."

"Dead Ant."

"Ant Soup."

"Anteater Blueplate Special."
I said rotates not flips LOL.
Night folks .
__________________
"The cure for anything is salt water: sweat, tears or the sea." Isak Dinesen
"To me the simple act of tying a knot is an adventure in unlimited space." Clifford Ashley
Seaworthy Lass is offline   Reply With Quote
Old 10-01-2013, 18:26   #282
Eternal Member
 
wolfenzee's Avatar

Join Date: Feb 2008
Location: Port Ludlow, WA (NW corner of Puget Sound)
Boat: 30' William Atkin cutter
Posts: 1,496
Send a message via ICQ to wolfenzee
Re: Distinct Activities: Shackled by a Common Name?

Quote:
Originally Posted by CaptForce View Post
True, but also keep in mind that an extremely accurate GPS costs less than a fairly accurate sextant. I agree that there is a huge amount of overpriced, color monitor, big screen, touch pad, interfaced, multi-screend stuff on the market, It is very easy to pay a modest sum for the best data if you are not one who swoons over glitz!
And a used hand held GPS (about $30) connected to a laptop, running free nav software (downloadable from NOAA...the same place you can down load the free charts from)......
Yeah and I bought a $1200 Tamaya sextant on e-bay, that happened to have the name SAURU on it (made by Tamaya)...for $40, person just didn't know what they had
__________________
"It is better to die living than live dieing" (Tolstoy para-phrased by Jimmy Buffet)
"Those who think they know everything piss off those of us who do"
wolfenzee is offline   Reply With Quote
Old 10-01-2013, 20:07   #283
Moderator
 
Seaworthy Lass's Avatar

Cruisers Forum Supporter

Join Date: Oct 2008
Boat: Aluminium cutter rigged sloop
Posts: 12,811
Re: Distinct Activities: Shackled by a Common Name?

OK, I lay awake and all I could think about were ants and treadmills. Counting sheep didn't help, so I am back online .

Andrew, I think the answer lies in breaking down the current into components. All that we are interested in is the component that is perpendicular to the 'direct line over ground between departure and destination points' (whatever you call that in navigation terms). The other component will just speed up or slow down our speed over ground.

So if these perpendicular components cancel out for the journey, our heading in a boat travelling at a constant speed needs to be the same as the direction of the destination point from the departure point (and in the treadmill analogy the ant heads in a perpendicular track). If the perpendicular components don't add up then the heading is different (and the ant's path over the treadmill is at an angle).

Thinking about the treadmill rotating around just does your head in LOL.

Edited to add:
I guess what I am trying to say is that the treadmill is just equivalent to the component of the current perpendicular to the initial direction to the destination, not the total current.
__________________
"The cure for anything is salt water: sweat, tears or the sea." Isak Dinesen
"To me the simple act of tying a knot is an adventure in unlimited space." Clifford Ashley
Seaworthy Lass is offline   Reply With Quote
Old 10-01-2013, 21:01   #284
Moderator
 
Seaworthy Lass's Avatar

Cruisers Forum Supporter

Join Date: Oct 2008
Boat: Aluminium cutter rigged sloop
Posts: 12,811
Re: Distinct Activities: Shackled by a Common Name?

A more correct analogy for the total movement during the journey is not a treadmill at all, but a disc that is capable of moving in any direction in the horizontal plane. The ant's starting point on the edge of the disc is at the starting point of the journey. The destination point on the disc is where the edge of the disc will first contact the required point of arrival and the ant is capable of reaching it given it's speed.

The ants path along that disc is always in a straight line for the quickest journey.

How does that sound?
__________________
"The cure for anything is salt water: sweat, tears or the sea." Isak Dinesen
"To me the simple act of tying a knot is an adventure in unlimited space." Clifford Ashley
Seaworthy Lass is offline   Reply With Quote
Old 11-01-2013, 03:47   #285
Registered User

Join Date: Feb 2012
Posts: 2,441
Re: Distinct Activities: Shackled by a Common Name?

I think it would be a good idea to go back to your bed, Lass !

Sleep deprivation can trigger novel insights, but IME you can never be sure until they're reassessed in the cold clear light of dawn...
__________________

__________________
Andrew Troup is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:34.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.